1. Field of the Invention
The present invention relates to a spindle control apparatus for a disk player which reads out data recorded on a disk called "CD-ROM".
2. Description of Background Information
On a CD-ROM, a vast amount of data such as data of video signal can be recorded. For instance, data for a high-definition still picture file would amount to about 4 Mbytes (megabytes) per picture without data compression. To read out such a high-definition still picture file at a normal reading velocity, it takes approximately 26 seconds per picture, so that over-all reading time becomes significantly long. In this respect, although data compression is normally performed to reduce the amount of data per picture, if the compressing amount is increased to further reduce the amount of data per picture, the picture quality will be deteriorated. If the velocity is increased to read a greater amount of data faster, the total reading time is shortened and it becomes unnecessary to increase the degree of the data compression. Through this method, prevention of the above-mentioned deterioration of the picture quality is possible.
In a picture file, audio data is often recorded with video data. For instance, if audio data is recorded on the basis of CD-DA, the same system as a digital audio disk called "CD", it is necessary to read out the audio data at the normal reading velocity. Therefore, a disk player which reads out recorded data from a CD-ROM needs to be designed to allow selection between two reading velocities: a reading velocity in high-velocity mode for reading out a vast amount of data, such as video data, in a short period of time, and a reading velocity in normal mode for reading out ordinary audio data.
In recording motion picture data, it is necessary to compress data using a method called "DVI", or the like because the data transfer rate at the normal reading velocity is as low as about 150 Kbytes (kilobytes) per second. The resolution of the picture is considerably lower than that of the picture provided by the NTSC system. To improve the picture resolution, the reading velocity needs to be increased for raising the data transfer rate, which reduces the amount of data compression. However, this method is undesirable since it will shorten the whole playing time of a CD-ROM disk.
In this respect, it is required that motion picture data has proper resolutions for different uses. For instance, when there are three reading velocities, namely, the normal reading velocity, a double reading velocity twice as fast as the normal reading velocity, and a quadruple reading velocity four times faster than the normal reading velocity, data may be recorded as follows:
a) At the normal reading velocity, it is possible to read out audio data recorded on the basis of the CD-DA and motion picture data, which has low resolution but ensures a long playing time. PA1 b) At the quadruple reading velocity, it is possible to reproduce motion picture data, which has high resolution but has a short playing time. PA1 c) At the double reading velocity, motion picture whose resolution and playing time are between those of the cases (a) and (b) respectively.
In the case where three types of data having the aforementioned three reading velocities are recorded on a CD-ROM disk in mixture, locking of the spindle servo is performed after the velocity is accelerated or decelerated toward one of a plurality of normal maximum rotational velocities for different types of recorded data as disclosed in Japanese Patent Application Laid-Open No. Sho 62-243166. In that case, the locking should be effected to two different values. This, however, resulted in a longer time for searching recorded data.